Archean to Paleoproterozoic evolution of the Crixás greenstone belt, Central Brazil: Insights from two contrasting assemblies of metaigneous rocks

Caio C.A. Borges, Catarina L.B. Toledo, Adalene M. Silva, Jason Kirk, Joaquin Ruiz, Farid Chemale, Renan G. Souza, Bruno A. Santos, Marcelo P. Campos, Luana M. Campos, Anderson M. Santos

Research output: Contribution to journalArticlepeer-review

Abstract

The Archean-Paleoproterozoic Crixás greenstone belt is one of the most important components of the Crixás-Goiás Domain, the oldest crustal segment of the Central Brazil Goiás Massif. This gold-bearing greenstone comprises amphibolite facies ultramafic-mafic metavolcanic rocks overlaid by a low-grade metasedimentary succession associated with rocks of intermediate composition. We present new integrated geochemical and isotopic data of the metaigneous rocks to characterize the stages of magmatism and delineate the petrogenetic processes and tectonic environment of the different units. The data give important insights into the geological evolution of the Crixás greenstone belt during the Archean and Paleoproterozoic, including that the Crixás greenstone belt consists of genetically and temporal unrelated rocks that are spatially associated in a structural framework marked by stacking and imbrication. Two lithological assemblies were described: i) a Mesoarchean komatiite-tholeiite association formed by heterogeneous mantle plume melting in an oceanic plateau setting, and ii) a Rhyacian intraoceanic arc association. These units are allochthonous and override an Archean crustal basement dominated by granites and gneisses of mostly TTG composition. Chemical composition of the komatiites is similar to the Barberton-type Al-depleted komatiites, whilst the basalts consist of high-Mg tholeiites with flat chondrite-normalized REE patterns and immobile trace element systematics that resemble Phanerozoic oceanic plateau lavas. Eruption age of the ultramafic and mafic lavas is roughly estimated at ~3.0 Ga, based on previously published Sm[sbnd]Nd and Pb[sbnd]Pb isotopic studies, whereas whole-rock Re[sbnd]Os isotopic data of samples of komatiite and basalt presented here yielded a 2609 ± 65 Ma isochron age. This younger age may reflect a Neoarchean overprinting event associated with metasomatic Re-addition recorded in the lower ultramafic-mafic metavolcanic rocks, possibly related to the late stages of the cratonization of the Crixás-Goiás Domain during the emplacement of the youngest Archean granites of the region (~2.70 Ga). Newly described andesites and diorites possess a subduction zone fingerprint. LA-ICP-MS U[sbnd]Pb zircon dating of an andesite sample provided an upper intercept Concordia age of 2172.2 ± 12.7 Ma, constraining the age of the intermediate magmatism. Therefore, these rocks are correlated with the Rhyacian syn-orogenic poorly-sorted graywackes and carbonaceous phyllites of the greenstone's upper stratigraphy. Andesites and diorites have homogeneous Paleoproterozoic two-stage Nd model ages of 2.28 to 2.26 Ga and positive initial εNd values of +2.34 to +2.69, indicating a juvenile nature for the arc magmatism. Re[sbnd]Os geochronology of gold-related arsenopyrite from a metasedimentary rock-hosted massive sulfide provided an age of 2137 ± 11 Ma, suggesting that the mineralization is also coeval to the Rhyacian collisional stage.

Original languageEnglish (US)
Article number106493
JournalLithos
Volume404-405
DOIs
StatePublished - Dec 1 2021

Keywords

  • Al-Depleted Komatiite
  • Crustal Growth
  • Goiás Massif
  • Greenstone Belt
  • Oceanic Plateau Basalt

ASJC Scopus subject areas

  • Geology
  • Geochemistry and Petrology

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